Extrusion apparatus



June 24, -1947. v F. J. FlELlTZ 2,422,722

EXTRUSION APPARATUS Filed March 5, 1946 [N VENTOR FREDERICK J. FIE'LITZmjd k q ATTORNEY Patented June 24, 1947 EXTRUSION APPARATUS Frederick J.Fielitz, North Arlington, N. J., as-

signor to E. I. du Pont de Nemours & Company, Wilmington, Del., acorporation of Delaware Application March 5, 1946, Serial'No. 652,087

3 Claims.

This invention relates to improvements in extrusion apparatuses and,more particularly,to the hopper assembly in screw stuffers used forextruding plastics.

The conventional screw stufier comprises a cylinder, a screw centrallypositioned and rotatable therein for extruding plastic from one end ofthe cylinder, and a hopper adjacent the other end of the cylinderthrough which the plastic is fed to the screw. In these screw stuifers,plastic stock is fed by the operator into the hopper, from which pointthe stock is engaged by the screw and directed down into the cylinder tobe extruded. A disadvantage of this method of operation is that usuallyplastic stock pinched off between the screw and the edge of the hopperbu lds up in the hopper until it prevents further feeding of new stockby clogging the hopper. Another disadvantage is that a materialvariation in the feeding of certain plastic stock, particularlycellulose nitrate, results in variation in the caliper of the productdue to varying extrusion pressure. Such a variation in feeding, wheninflammable stock is being extruded, sometimes unduly compresses airpockets in the stock and causes it to flash, thereby jeopardizingpersonnel and equipment.

It will be seen, therefore, that the conventional screw stufler not onlyis inefficient to a certain extent due to the clogging up of the hopperand also delivers a certain amount of imperfect extruded stock but italso exposes the operator to the danger of the stock flashing and, inaddition, the operator in endeavoring to unclog the hopper while thescrew stuifer is in operation, runs the risk of getting his hands caughtin the screw. This is a not infrequent cause of industrial accidents inshops using these machines.

An object of the present invention is to provide 'an improved hopperassembly for screw stuffers. A further object is to provide animprovement in the construction of the hopper of a screw stufier whichwill increase the uniformity and rate of feed of plastic, thusincreasing the efficiency of the apparatus and improving the productextruded therefrom. A further object is to provide such a constructionwhich will tend to prevent an operator from getting his hands caught inthe screw while feeding plastic into the hopper. Other objects will beapparent from the description of the invention given hereinafter.

The above objects are accomplished according to the present invention bymounting in the hopper of a screw stuffer a device for regulating thefeed of plastic into the cylinder of the screw wellknown screw stufiersused stuffer, the device essentially comprising a plate rigidly mountedin the bottom of the hopper to close off a portion of it and at the sametime to form a relief zone between the plate and the screw in whichthere is an extrusion compression exerted on the plastic somewhat lessthan the extrusion compression exerted on the plastic in the cylinder.

More specifically, the invention comprises a plate mounted in the hopperof a screw stuffer at the bottom thereofand closing off a portion, up toone-half, of the hopper bottom at the end nearest the discharge end ofthe cylinder of the screw stuffer, the face of the plate adjacent thescrew of the screw stuifer having a radial curvature substantially thesame as the curvature of the wall of the cylinder. The plate ispositioned with the curved face approximately parallel to the cylinderwall and the distance, measured radially with respect to the axis of thescrew, between the crests of the screw and the plate increasing in thedirection of extrusion, thus forming the desired relief Zone.

The invention will be more fully described with reference to theaccompanying drawing wherein identical reference numerals are used todes-- ignate similar parts in the various views and wherein:

Fig. 1 is a section on the line l-l of Fig. 2 of a portion of a screwstufier in which is installed a specific embodiment of the instantinvention;

Fig 2 is a section on the line Z-2 of Fig. 1; and

Fig. 3 is a perspective View of the plate ll] shown in Figs. 1 and 2.

Referring particularly to Figs. 1 and 2, reference numeral l designatesthe cylinder of a conventional screw stuifer provided with the heatingjacket 2. The usual screw 3 is centrally positioned and rotatablymounted in the cylinder I, Fig. 1 merely showing that portion of thescrew stufier necessary to illustrate the present invention. Thedelivery end of the stufier is to the left as viewed in Fig. 1. Thecylinder I is provided with the conventional hopper 4, frequently madeas an integral part therewith but not necessarily so, which provides theopening through which plastic is fed to the screw 3 which, in turn,forces it through the cylinder I. It should be noted that the length ofthe hopper opening is the distance A as indicated in Fig. 1. Theconstruction so far described is that of the in the plastic art.

Mounted in the hopper 4 is the device of the present invention forregulating the feed of plasporting iron I I attached to the walls' ofthe hopper 4 by the screws I2, the plate In being secured to the iron IIby one or more screws I3. The supporting iron II and the plate I!) maybe made as an integral piece if preferred. The plate I!) is shown inperspective in Fig. 3 and is provided with a curved face I4, the radialcurvature of this face I4 being substantially the same as that of theWall of cylinder I. The plate Iilis also tapered as illustrated in Fig.3 and, more clearly, in Fig. 1.

By referring to Figs. 1 and 2, it will be seen that the plate II] ispositioned so that the face I4 is approximately parallel to the wall of.the cylinder I and the edge of the plate IIJ farthest from the deliveryend of the cylinder I clears the crest I5 of the screw 3; the plate Icloses off completely a portion of the bottom of the hopper 4 at the endthereof nearest the discharge end of the cylinder I. Actually, it ispreferred that the plate Ill be positioned so that its curved face I4-is not precisely parallel to the wall of the cylinder but rather formsthe arc of a circle slightly eccentric in the direction of the screwturns (see direction arrow, Fig. 2) with respect to the circle formed bythe wall of the cylinder I. This slight eccentricity is shown in Fig. 2.The reason for having the plate positioned with this slight eccentricityis that it tends to increase the smooth operation'of the screw stufferbut the apparatus functions satisfactorily if the plate In is positionedso that its curved face I4=is exactly parallel to the wall of cylinderI, that is, the curved face I4 forms thearc of a circle exactly concen-V tric with respect to the circle formed by the wall of cylinder I.

An essential feature of the present invention is the positioning of theplate I!) so that the distance between the face I4 and a line runningalong the crests I5 and IBzo'f the screw 3, measured radially withrespect to the axis of the screw 3, increases in the directiono'fextrusion. It has been found that, under normal circumstances, thedistance should increase along a line running at an angle of 1 to to theaxis of screw 3, pref erably at an angle of 4 to '8" and, specifically;at an angle of 5.

A second feature of the invention is that the plate ID at the edgefarthest from the delivery end'of cylinder I should be spaced slightlyfrom the crest of the screw 3. That is, measured radially with respectto the axis 'of' the screw 3, there'shouldb'e an appreciable clearancebetween the face of plate I'Il' and the crest I5 of screw 3, as viewedin Fig. 1. Usually, this clearance should bebetween 64 and /1 of" aninch and, preferably, between /az and A of'an inch, with a distance of/32 of an inch specifically'preferred.

It will be noted that the plate- I Ii'is positioned so as to block off aportion of the bottomof the hopper 4 at the end thereof nearest thedelivery end of the cylinder land, at the same time,

to form a zone in combination with the screw 3 by one flute of the screw3 is engaged by the following flute and carried under the plate Ill,thus preventing build up of stock in hopper 4. The stock is thengradually and uniformly carried by the screw through the zone of lowerextrusion compression into the cylinder I where it goes under fullextrusion compression without the sudden and undesirably highcompression frequently encountered in the conventional design screwstuffers.

While the invention has been described more or less with reference tothe particular embodiment thereof illustrated in the drawing, it is byno means restricted to the specific construction shown. The proportionof the hopper bottom closed 01f by the plate I?! may be varied greatlybut will not exceed one-half of the bottom of the hopper in any stufferof normal design now on the market. It is not important that the plateit cover any particular proportion of the length of the screw 3.. Toform an effective 'zone of relatively low extrusion compression theplate will ordinarily close off at least one-fourth of the hopperalthough advantage of the present invention can be gained to a lesserextent bythe use of a plate closing off even less of the hopper opening.

The spacing of the plate Iii above the screw 3 and the angle of theplate with respect to the of the screw have, been indicated above asparticularly adapted for the extrusion of cellulose nitrate stock atconventional temperatures, that is, with the stock fed into the hopperat about F. and the cylinder maintained in the neighborhood of 210 F.Those skilled in the art will readily appreciate that the clearance ofplate It! above the crests of the screw 3'c0ulcl be: greater if it weredesired to-w'ork stock of unusually stiff consistencyor less if thestockwere exceptionally plastic either due to its particular composition orthe temperature employed; However, the measurements given afford areliable guide for the plastics customarily worked in screw stufiers;The pitch and speed of the screw are also other but relatively minorfactors in determining the optimum positioning of the plate Ill in anygiven circumstances, The specific manner in which the plate ID is heldin p'o'sition'in the hoppe'rob'viously is not critical in thisinvention.

This invention introduces many advantages in the art ofextruding'pla'stic materials'by'mea'ns of screw stuffers; Because of thefold b'ack' action of the plate on the plastic stock, the rate offeeding'and consequent rate of extrusion are increased significantly.Plastic is compressed in thecylind'er of the stuffer gradually ratherthan suddenly andthis greatly improves the appearance and properties ofthe extruded'plastic products. Further, the extrusion of plastic in anapparatus constructed according to the present invention is much saferbecause the necessity for the operator to apply force in order tofe'ed'th'e stock into the cylinder of the s't'uif'e'r' has beensubstantially eliminated and, even if force is applied, the guard actionof the plate tends'to prevent the operator from getting a han'd caughtin the screw. Also, the possibility of inflammable plastic stockflashing has been minimifzeddue to the uniform conveyance of the plasticinto the cylinder.

It will be apparent that the present apparat'us does not involvejanyappreciable-initialexp'ens'e and; as far as maintenance expense isconcerned, thepresentinve'ntion adds nothing appreciable to this.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

I claim:

1. A screw stuifer comprising a cylinder, a screw centrally positionedand rotatable therein for extruding plastic from one end of saidcylinder, a hopper adjacent the opposite end of said cylinder throughwhich plastic is fed to said screw, a device for regulating the feed ofplastic into said cylinder, said device comp-rising a plate rigidlymounted in said hopper immediately above said screw and extending over aportion thereof and closing off a portion of said hopper at the sidethereof nearest the discharge end of said cylinder, the face of saidplate adjacent said screw having a radial curvature approximately thesame as the curvature of the wall of said cylinder and the plate beingpositioned with said face approximately parallel to the wall of saidcylinder and the distance, measured radially with respect to the axis ofsaid screw, between the crests of said screw and said face increasing inthe direction of extrusion whereby a relief zone is formed between saidplate and screw in which there is an extrusion compression exerted onthe plastic less than the extrusion compression exerted on the plasticin said cylinder.

2. A screw stuffer comprising a cylinder, a screw centrally positionedand rotatable therein for extruding plastic from one end of saidcylinder, a hopper adjacent the opposite end of said cylinder throughwhich plastic is fed to said screw, a device for regulating the feed ofplastic into said cylinder, said device comprising a plate rigidlymounted in said hopper immediately above said screw and extending over aportion thereof and closing off a portion of said hopper bottom at theside thereof nearest the discharge end of said cylinder, the face ofsaid plate adjacentsaid screw having a radial curvature approximatelythe same as the curvature of the wall of said cylinder and the platebeing positioned with said face approximately parallel to the wall ofsaid cylinder and the distance, measured radially with respect to theaxis of said screw, between the crests of said screw and said face beingfrom & inch to inch at the edge of said plate farthest from thedischarge end of said cylinder and increasing along a line at an angleof 1 to 10 to the axis of said screw whereby a relief zone is formedbetween said plate and screw in which there is an extrusion compressionexerted on the plastic less than the extrusion compression exerted onthe plastic in said cylinder.

3. A screw stuffer comprising a cylinder, a screw centrally positionedand rotatable therein for extruding plastic from one end of saidcylinder, a hopper adjacent the opposite end of said cylinder throughwhich plastic is fed to said screw, a device for regulating the feed ofplastic into said cylinder, said device comprising a plate rigidlymounted in said hopper immediately above said screw and extending over aportion thereof and closing off a portion of said hopper bottom at theside thereof nearest the discharge end of said cylinder, the face ofsaid plate adjacent said screw having a radial curvature approximatelythe same as the curvature of the wall of said cylinder and the platebeing positioned with said face approximately parallel to the wall ofsaid cylinder and the distance, measured radially with respect to theaxis of said screw, between the crests of said screw and said face beingapproximately of an inch at the edge of said plate farthest from thedischarge end of said cylinder and increasing along a line at an angleof approximately 5 to the axis of said screw whereby a relief zone isformed between said plate and screw in which there is an extrusioncompression exerted on the plastic less than the extrusion compressionexerted on the plastic in said cylinder.

FREDERICK J. FIELITZ.

REFERENCES CITED The following references are of record in the,

file of this patent:

UNITED STATES PATENTS Number Name Date 1,066,722 Ganzhorn July 8, 19131,066,723 Ganzhorn July 8, 1913

